This invention relates to power transmissions having a plurality of speed ratios, and more particularly, to a power transmission having a variable ratio belt drive for providing a variable speed ratio range in a multi-ratio transmission.
A conventional variable ratio power transmission has a variable belt drive mechanism disposed in series with the transmission input; i.e., torque converter and planetary gear arrangement, which provides forward and reverse drive ratios either into or out of the variable belt drive mechanism. With these arrangements, the variable belt drive mechanism transmits the high torque values required to launch the vehicle during operation in the low forward ratio and the reverse ratio. These torque values can be very high when a vehicle is fully loaded or started on an upgrade.
The prior art transmissions therefore, must size the variable belt mechanism to have sufficient torque capacity to continuously transmit these high torque loads. This generally becomes the limiting factor in the design of a transmission using a variable belt drive. In automotive passenger vehicles, this factor results in variable belt drive mechanisms being utilized only in small vehicles having a low GVW and a short wheel base.